BSc (Hons) I Experiment 14: Refractive Index of Liquid by Liquid Lens Method Concave Mirror Method
Apparatus Biconvex lens, concave mirror, plane mirror, spherometer, stand, long pin, metre rule, the liquid used is water Information Before starting the experiment, you need to consult some literature about i) how to find the focal length of a convex lens using a long pin, a plane mirror and the method of no parallax; ii) how to find the radius of curvature of a surface using a spherometer; iii) how to find the radius of curvature of a concave mirror using a long pin and the method of no parallax. a) The focal length of a combination of two lenses in contact is given by 1 1 1 F f1 f 2 The focal length of a lens in air is given by 1 1 1 ( 1)( ) f r1 r2 where η is the refractive index of the lens material, while r1 and r2 are the radii of curvatures of the lens surfaces. When an object is viewed at the bottom of a layer of liquid, the refractive index η of the liquid is given by Re alDepth ApparentDepth
In the first part of the experiment, the focal length f1 of the convex lens and the focal length F of the liquid/glass lens combination are found, using a plane mirror, a long pin and the method of no parallax. Thus the focal length f2 of the liquid lens can be calculated. The radius of curvature of the liquid lens can be found by using the spherometer. Hence the refractive index of the liquid can be calculated.
In the second part of the experiment, the position of no parallax with the pin and the concave mirror, will give the radius of curvature of the concave mirror. The experiment is repeated with a few drops of water in the concave mirror. The two readings behave as the real depth and the apparent depth of the liquid used. Hence the refractive index of the liquid can be found.